This invention relates to hand tools, and more particularly to tools utilizing a pair of jaws for receiving a workpiece therebetween.
Common elements of locking pliers, locking wrenches and similar tools employing some form of locking toggle-actuation are a pair of stationary and movable jaws adapted to lock a workpiece therebetween. A mechanism with an adjusting element acting on the movable jaw is usually provided to adjust a gap between the jaws and to bring them into possible initial contact with a workpiece before huge forces of the toggle action are generated and applied.
The tools of the type presently described are usually used in the circumstances when fast and efficient adjustment of the gap between the jaws is not only highly desirable but absolutely necessary. One example of such use is a conveyor welding operation where a welder has a very short time for adjustment of the tool between welding together two separate pairs of elements having different dimensions. In this situation, it is extremely important to adjust the gap between the jaws of the locking tool to accommodate the dimensions of a new pair of elements as soon as possible.
A known type of prior art device makes such adjustment of a gap between the jaws by means of rotation of a single threaded, single pitch adjustment screw to which the movable jaw is connected directly or indirectly. This method and means of adjustment are necessarily slow and time consuming and result in loss of valuable time in adjusting the tools from one size to another.
U.S. Pat. No. 2,681,583 recognizes the necessity of fast adjustment of the spacing between adjustable jaws of wrenches. It also recognizes that the conventional means of adjustment are slow and time-consuming, since these methods depend on the speed of rotation of the threaded shafts. This patent specifically teaches that use of the threaded screw member which advances longitudinally while it is rotated within the threaded opening of the tool, is slow, tedious and time-consuming and should be avoided. In view of that, this patent provides a device in which the space between the wrench jaws is adjusted by a straight line reciprocating manipulation of the control rods. When it is desired to bring the jaws from the spread-apart to the locked position, the movable jaw is typically swung manually towards the fixed jaw until the desired spacing is achieved. Thereupon, a control rod is grasped and pushed inwardly and longitudinally to butt against the rear parts of the adjusting means. A pivotally movable arrangement is used to secure the position of the rod and to lock a gap between the jaws.
U.S. Pat. No. 2,643,567 to Johnson provides another hand tool to effect faster adjustment of the gap between the jaws. In this patent, fixedly mounted in the tubular outer end portion of the fixed handle is a bushing having a threaded bore in which is threadedly engaged a tubular adjusting screw having right-hand external threads. The adjusting screw projects rearwardly from the handle member and the projecting portion of the screw has a turning knob. The adjusting screw is formed with internal threads engaged by left-hand threads provided upon a toggle holder.
U.S. Pat. No. 3,590,669 to Maranco discloses a locking hand tool having a higher rate of advancement of the adjusting screw. However, such rate of adjustment is the result of the use of the large lead angle of the thread combined with the large diameter of the screw.
U.S. Pat. No. 4,389,145 to Capuano discloses an internally threaded fastener which includes a body having an opening with a sidewall. Coarse and fine threads are formed in the sidewall of the nut body. The turns of these threads are intermingled to enable them to engage a fastener having either a coarse or fine external thread. Capuano specifically teaches that the terms "coarse" and "fine" are used in the patent to distinguish between thread convolutions having a greater and lesser number of turns per unit of axle length.